But the small furnace uncovered at Ballinvinny, Co. Cork, is a quiet trace of Iron Age metalworking, found not through deliberate archaeological investigation but because a road had to be built. When contractors began preparations for the N8 Glanmire-Watergrasshill Bypass in 2001, excavation revealed a circular feature only about 0.34 metres across and a minimum of 0.07 metres deep, its edges already worn down by centuries of farming. Inside it were two distinct layers: an upper fill of soft, black, charcoal-rich material mixed with slag, and beneath that a beige-grey clay scorched in patches, the kind of evidence left behind when intense, repeated heat has worked its way into the ground.

Analysis of the slag pointed to the processing of bog iron, a raw material obtained from iron-rich deposits that form naturally in waterlogged ground and which was widely used across early medieval and prehistoric Ireland before more conventional ore sources were exploited. Whether the feature functioned specifically as a bowl-shaped smelting furnace, a shallow pit designed to concentrate heat and reduce ore to workable metal, could not be confirmed with certainty. What radiocarbon dating of the charcoal samples did establish was an age of roughly 1,990 years, plus or minus 60 years, placing activity here in the Iron Age. The excavator was R. Sherlock, whose reports on the site were compiled in 2003. Notably, the Ballinvinny furnace did not stand alone: a separate metalworking site was excavated approximately 900 metres to the north-east, suggesting that this part of Cork was home to a small concentration of ironworking activity during the same broad period.